A tyre for vehicle wheels generally comprises a carcass structure comprising at least one carcass ply having end flaps engaged with respective annular anchoring structures. A belt structure is associated in a radially outer position to the carcass structure, comprising one or more belt layers, arranged in radial superposition with respect to each other and with respect to the carcass ply, having textile or metallic reinforcing cords with crossed orientation and/or substantially parallel to the circumferential development direction of the tyre. A tread band is applied in a position radially outer to the belt structure, also made of elastomeric material like other semi-finished products making up the tyre. Respective sidewalls of elastomeric material are further applied on the lateral surfaces of the carcass structure, each extending from one of the lateral edges of the tread band up at the respective annular anchoring structure to the beads. In “tubeless” tyres, the carcass ply is internally coated by a preferably butyl-based layer of elastomeric material, usually called “liner” having optimal airtight characteristics and extending from one to the other of the beads.
The term “elastomeric material” is used to designate a composition comprising at least one elastomeric polymer and at least one reinforcement filler. Preferably, such composition further comprises additives such as, for example, a cross-linking agent and/or a plasticiser. Due to the presence of the cross-linking agent, such material can be cross-linked by heating, so as to form the final manufactured article.
The expression “noise reducer element” means an element which, once associated with a radially inner surface of a tyre, has the ability to attenuate the noise produced by the tyre itself during use. This ability can be conferred to said element by the type of material, or materials, with which said element is made and/or by the shape of the same. Such noise reducer elements usually consist of blocks of porous material such as, for example, foamed polymeric material.
By “equatorial plane” of the tyre it is meant a plane perpendicular to the axis of rotation of the tyre and which divides the tyre into two symmetrically equal parts.
The terms “radial” and “axial” and the expressions “radially inner/outer” and “axially inner/outer” are used referring to a direction perpendicular and a direction parallel to the axis of rotation of the tyre, respectively. The terms “circumferential” and “circumferentially” are used with reference to the direction of the annular development of the tyre, namely the rolling direction of the tyre.
Document EP2067633 describes a noise reduction device and a tyre, in which the tyre vibration and noise can be reduced. The noise reduction device comprises two main sound-absorbing elements adapted to change the sectional area of a cavity of the tyre and two auxiliary sound-absorbing elements arranged between the two main sound-absorbing elements.
Document EP2123491 describes a noise reduction device comprising at least one sound-absorbing element made of porous material attached to the inner surface of the tread portion of the tyre. The sound-absorbing element may include a plurality of parts arranged spaced apart along a circumferential direction of the tyre.